The flight instructor reported that, while en route on an instrument flight plan, about 4000 ft, they entered a cloud where a flock of large black birds were circling. A bird impacted the stabilator, he disengaged the autopilot and checked the flight controls for any adverse effects, which none were observed. The instructor then elected to returned to the departure airport and landed without further incident.

The airplane sustained substantial damage to the stabilator.

The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.